Automated media storage libraries are known for providing cost effective access to large quantities of stored media. Tape cartridges containing a moveable magnetic tape are often used in automated data storage libraries. Tape media, such a magnetic tape, is a common medium for the storage of data to be utilized by a computer. Magnetic tape has found widespread use as a data storage medium because it provides a relatively inexpensive solution for storing large amounts of data.
Magnetic tape typically includes one or more prerecorded servo tracks to allow precise positioning of a tape head with respect to those prerecorded servo tracks. Servo sensors disposed on the tape head are used to track the recorded servo tracks. The tape head comprises one or more read/write elements precisely positioned with respect to those servo sensors. In certain embodiments, the one or more prerecorded servo tracks include longitudinal position signals disposed along the length of the tape medium.
What is needed is a method to monitor the unwinding of a tape from a supply tape reel onto a take-up reel to assure that the tape drive discontinues tape movement when an end of the tape is approaching. Applicants' method monitors the movement of a tape from a supply reel to a take-up reel by maintaining a running count of the rotations of the supply reel, maintaining a running count of the rotations of the take-up reel, and monitoring longitudinal position signals disposed in one or more servo signals written to the tape.